Method using composition to reduce cutting head wear

ABSTRACT

A method of reducing wear in a cutting head of a tunnel boring machine, by means of the addition at the cutting head of a foamed aqueous liquid composition, which comprises a foaming agent and a lubricant, the lubricant being selected from the group consisting of high molecular weight polyethylene oxides and bentonite. Preferred foaming agents are anionic and nonionic surfactants. Wear rates of cutting elements of TBMs boring in hard rock are considerably reduced. A wear-reducing foamable concentrate is also described.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a national stage application of InternationalApplication No. PCT/EP2003/009718, filed Sep. 2, 2003, which claims thebenefit of Application No. GB 0221171.2, filed Sep. 13, 2002, from whichapplication priority is claimed.

This invention relates to a method of boring a tunnel in hard rock andto compositions for assisting such boring.

The boring of tunnels in hard rock, such as limestone and metamorphic origneous rocks, has always presented more problems than has boring insofter rock. The most commonly used method of tunnel boring in such rockhas been the drilling of blast holes, followed by blasting withexplosives. It has been desired to use tunnel boring machines (TBMs),machines with large diameter cutting heads (sometimes in excess of 10m), for tunneling in hard rock. The major problem of TBM use in suchrock is the rapid wear of the cutting elements (hardened steel discswhich protrude from the cutting head) and the necessity for frequentreplacement, a disadvantage from both operational and economic points ofview.

It has now been discovered that the use of a particular composition canreduce this wear considerably, permitting more efficient and economicboring in hard rock with a TBM. This invention therefore provides amethod of reducing wear in a cutting head of a tunnel boring machine, bymeans of the addition at the cutting head of a foamed aqueous liquidcomposition, which comprises a foaming agent and a lubricant, thelubricant being selected from the group consisting of high molecularweight polyethylene oxides and bentonite.

The foaming agent may be any foaming agent, that is, any material that,when agitated in water, will cause stable foam to form. It is possibleto use more than one such foaming agent in a composition for use in thisinvention. A wide variety of such materials is known to the art. Thepreferred materials for use as foaming agents in this invention aresurfactants, that is, materials that have both hydrophilic componentsand hydrophobic components. Although any suitable surfactant can beused, it has been found that, for the purposes of this invention, thesurfactants that work best are anionic or nonionic types, and these arethe preferred surfactants.

If the surfactant is an anionic type, it is preferably asulphate-containing surfactant, more preferably an alcohol sulphate, andmost preferably a lauryl sulphate. Many suitable materials are known tothe art, an example of a particularly preferred material beingmonoisopropanolamine lauryl sulphate (available commercially, forexample, under the trade name “Sulfetal” Cjot 60).

While the performance of anionic surfactants is excellent, their use issometimes undesirable if environmental considerations are important. Forenvironmental reasons, it is preferred that the foam be short-lived,that is, that it remain a foam only for the time between its generationand the removal of the foamed liquid from the cutting face. The foamfrom anionic surfactants can be so stable and durable that it can besometimes found in rivers remote from the job site. In such cases,nonionics are preferred; their performance on the job site is no lessexcellent, but they biodegrade more quickly and any foam generated lastsfor a relatively short time. In addition, the breakdown components ofthe nonionic surfactants are considerably less harmful than those of theanionics, and they therefore represent less of a toxicological hazard toplant and animal life.

Examples of effective nonionic surfactants suitable for use in thisinvention include alkanolamides, aminoxides, ethoxylated alcohols,ethoxylated alkylphenols, ethoxylated esters, glucose and sucrose estersand derivatives thereof. Especially effective are the glucose andsucrose esters and their derivatives, particularly alkyl polyglucosides.Typical commercial examples of these include “Lutensol” (trade mark) GD70 (ex BASF) and “Glucopon” (trade mark) (ex Cognis).

The lubricant may be chosen from one of two different materials, both ofwhich are readily available commercially. By “high molecular weight”polyethylene oxide (PEO) is meant a PEO with a weight-average molecularweight of at least 1,000,000. Preferably the molecular weight is from2,000,000-8,000,000. Such materials have previously been used in theboring of tunnels with TBMs, but never in connection with hard rockboring. Typical commercial materials include POLYOX (registered trademark) WSR-301. A blend of different PEOs may be use, although, being apolymer, a PEO has a molecular weight distribution, and it is thereforealready inherently a blend of different materials.

The alternative lubricant is bentonite. This clay material is alreadywell known as a constituent of drilling muds, and it has also been usedin some TBM applications. However, its use in conjunction with thefoaming agents hereinabove described to achieve this particular end isnew. Any commercially-available bentonite is suitable for the purposesof the invention, a typical example being “Tixoton” (trade mark).

The compositions are prepared for use by the addition of a suitableamount of water. Although the supply of dry compositions istheoretically possible and is not excluded from this invention, it isimpracticable. One reason for this is that it introduces the task ofproducing the liquid composition on the job site—this can be difficult,especially with PEOs of high MW, which, although water-soluble, can bedifficult to dissolve. In addition, other commercially-availableadditives (further described hereinunder) are often supplied only insolution or suspension form.

There are two methods of overcoming these difficulties. The first is tosupply the compositions as a series of individual aqueous ingredientsthat can be metered in the correct individual proportions to arelatively large quantity of water for foaming. Thus, the PEO and/or thebentonite, the foaming agent and any optional ingredients (furtherdescribed hereinunder) are provided individually in aqueous form. Therequired containment and metering equipment is well known to the art anddoes not therefore need to be further described here. This method hasthe advantage of versatility—the quantities of ingredients can be variedto suit local conditions as they arise and any optional components canbe included or not included, as the case may be. It is even possible toinclude both types of lubricant (PEO and bentonite), and to change fromone to the other. The disadvantage is, of course, that a further pieceof equipment, with its associated cost and maintenance problems, isintroduced.

A more desirable method for most applications is to provide aconcentrate, an aqueous solution or suspension with a suitableproportion of the necessary ingredients, which is capable of being usedquickly and easily. It is no problem to dilute such a concentrate andfoam the diluted concentrate at a job site. Where the versatility of themetering approach previously outlined is not needed, this is muchpreferred, because of its simplicity of use and relative cheapness.

The quantities of ingredients referred to in the following paragraphsrelate to an aqueous composition which comprises the dry ingredientsplus sufficient water, either to render the individual ingredients inaqueous form for individual metering as hereinabove described, or forthe preparation of an aqueous concentrate, as hereinabove described. Thecompositions are made up to 100% with water. This does not include thefinal dilution and foaming water (for which quantities see p. 5).

In the case where PEO is used as lubricant, the quantities of PEO usedare from 0.1-3.0%, preferably from 0.4-2.0%, and more preferably from0.5-1.0% by weight of the concentrate. The equivalent quantities offoaming agent are from 2-40%, preferably from 5-30%, and more preferablyfrom 5-20%.

If bentonite is used as lubricant, the quantities are from 2-30%,preferably from 2-25%, and more preferably from 2-20%, and theequivalent quantities of foaming agent are from 2-40%, preferably from4-20%, and more preferably from 5-15%.

It is possible to add other ingredients to the compositions for use inthis invention. Two particularly useful ones are sequestering agents andfoam boosters. These are generally more effective in compositions wherePEO is the lubricant, but they can be used also with bentonite. Inaddition, in the preferred cases, they are more often useful withanionic surfactants; they have little effect with nonionics. This isespecially true of the sequestering agent.

The sequestering agent is present to counter any problems brought aboutby the use of hard water in the preparation of the final foamedsolution—hard water can cause the precipitation of the foaming agent andrender the composition useless. If there is no hard water present, asequestering agent is naturally not needed, but the addition of such anagent provides a composition which may be used in any water conditions,and which is therefore always ready for use in any circumstances. Anysuitable sequestering agent may be used, the quantities used being inthe range of up to 5%, preferably from 0.1-5%, more preferably from0.5-2%, and most preferably from 1-1.5%. An example of a sequesteringagent which is suitable for use in this invention is “Cublen” (trademark) K2523.

The foam booster may likewise be any suitable material. The quantitiesused are up to 10%, preferably from 0.1-10%, and more preferably from0.1-1%. An example of a foam booster which is suitable for use in thisinvention is “Aromox” (trade mark) MCD-W.

The invention also provides a wear-reducing foamable liquid concentrate,consisting of at least one lubricant selected from high molecular weightpolyethylene oxide and bentonite, and at least one foaming agent whichgives rise to short-lived foams, optionally also containing at least onesequestering agent and at least one foam booster, the quantities presentbeing respectively

(a) in the case of polyethylene oxide as lubricant:

-   -   0.1-3% polyethylene oxide;    -   2-40% foaming agent;    -   up to 5% sequestering agent; and    -   up to 1% foam booster;        and (b) in the case of bentonite as the lubricant:    -   2-30% bentonite; and    -   2-40% foaming agent;        by weight of the concentrate, the remainder being water.

In use, in the case of a concentrate, the concentrate is added to asuitable quantity of water and foamed, before being pumped to therotating cutting head and injected at the interface of cutting head androck. In the case of an individual ingredient metering system, therequired quantities of aqueous ingredients are metered to a suitablequantity of water and foamed. Typically, the concentrate/individualingredients previously described is or are diluted with water to give anaqueous composition having from 1-20%, preferably 1-10%, more preferablyfrom 1-8% and most preferably from 1-6% of concentrate/individualingredients.

This diluted composition is foamed by any convenient means to give avolume expansion of from 5-40, preferably from 5-20, more preferablyfrom 8-20 times the volume of the unfoamed material.

The actual dilution of the concentrate/individual ingredients and theamount to which it is foamed will vary considerably, depending on theparticular circumstances. Such factors as diameter of cutting head,number and location of injection nozzles and nature of rock will have amajor effect. The essential requirement is to maintain a layer of foamin contact with the rock face across the entire area of the cuttinghead. Achieving this requirement is a matter of routine experimentationand the skilled person will easily be able to do it. Typical figures fora concentrate of the type hereinabove described are from 0.5-10.0,preferably from 0.5-6.0, more preferably from 1-4 kg concentrate/m³ rockremoved. If individual aqueous ingredients are being added, equivalentquantities can easily be calculated. It is emphasized that these figuresare given only as a general guideline, and that certain conditions mayrequire lower or higher quantities of individual ingredients orconcentrate.

It is a surprising feature of this invention that the use of an aqueousliquid composition as hereinabove described results in a considerablereduction in wear of cutting elements in hard rock, leading to longercutting head life and less frequent replacement, and therefore betterand more economical tunnel boring. It is believed, without restrictingthe scope of this invention in any way, that the fine material producedat the drilling face of the TBM is bound together by the aqueous liquidcomposition and acts as a lubricant.

The invention is now illustrated by the following non-limiting examples.

Composition A (Using Anionic Surfactant)

The following ingredients are used:

“Polyox” WSR 301 polyethylene oxide, 0.83% weight-average molecularweight 4,000,000 (“PEO”) “Sulfetal” Cjot 60 surfactant  9.0% “Cublen” K2523 sequestering agent (“SA”)  0.3% “Aromox MCD-W foam booster (“FB”)0.15% water to 100%Compositions B and C (Using Nonionic Surfactant)

The compositions are as follows:

B C “Lutensol” GD 70 10.0% 10.0% “Polyox” WSR 301 0.9% bentonite 4.2%sodium bicarbonate 0.4% water to 100% to 100%Testing

A method of ascertaining the effectiveness of the compositions for usein this invention prior to use with a TBM, thereby saving time andmoney, requires the following apparatus:

PVC jar, 1 litre, wide mouth

test specimen

silicon carbide powder (0.841-1.19 mm)

The test specimen consists of three wheels of ST 50 steel of 50 mmdiameter and 14 mm thickness with a 10 mm diameter axial hole, the threebeing secured to an M10 bolt by any suitable means (such as nuts andwashers), such that there is about 14 mm space between adjacent wheels.

The procedure is as follows:

400 g. of the silicon carbide is mixed with quantities of water andcomposition and added to the jar. A test specimen, of which the weightsof the three individual wheels are accurately known, (to 0.001 g.) isthen added to the jar, and the jar is sealed, placed on a mill androlled for 3 hours at 125 rpm. The wheels are then weighed and the lossof weight (wear) is found.

The compositions A, B and C are tested in this way. In each case, thecompositions are diluted with water (5% composition in water) and 30 and60 g samples are foamed to give a volume expansion of 10 times. As acontrol, 60 g water is added to a 400 g sample of the silicon carbideand tested. The wear rates of the test specimens are as follows:

SiC + water 204 mg SiC + 30 g A 190 mg SiC + 60 g A 157 mg SiC + 30 g B129 mg SiC + 60 g B 115 mg SiC + 30 g C 123 mg SiC + 60 g C  90 mg

As can be seen, the wear rates are reduced, in some cases verysubstantially.

1. A method of boring hard rock by means of a tunnel boring machinecomprising hardened steel discs which protrude from the cutting head,wherein wear in the cutting head is reduced, comprising tunnel boring inhard rock, and adding at the cutting head while boring a foamed aqueousliquid composition injected at the interface of the cutting head and thehard rock, which composition comprises a foaming agent and a lubricant,the lubricant being selected from high molecular weight polyethyleneoxides.
 2. The method of claim 1, in which the individual ingredients ofthe foaming composition are dispensed in individual aqueous form intowater and are converted to foam.
 3. The method of claim 1 wherein thefoaming agent is at least one of anionic or nonionic surfactants.
 4. Themethod of claim 1, in which the composition is supplied as aconcentrate, which is diluted with water in situ, to provide the foamingcomposition.
 5. The method of claim 3, wherein at least one surfactantis nonionic and comprises at least one of alkanolamines, aminoxides,ethoxylated alcohols, ethoxylated alkylphenols, ethoxylated esters,glucose esters, sucrose esters or derivatives thereof.
 6. The method ofclaim 1, in which the polyethylene oxide has a weight average molecularweight of at least 1,000,000.
 7. The method of claim 4, in which theconcentrate is added in an amount of about 0.5 to about 10 kg/m³ of rockremoved.
 8. The method of claim 4, in which the wear-reducing foamableliquid concentrate also contains at least one of a sequestering agent orfoam booster, in which the components of the wear-reducing foamableliquid concentrate are present in the following amounts: 0.1% to 3%polyethylene oxide; 2% to 40% foaming agent; from greater than 0% to 5%sequestering agent; and from greater than 0% to 10% foam booster; byweight of liquid composition, the remainder being water.
 9. The methodof claim 8, in which the wear-reducing foamable liquid concentrate isdiluted in about 1 to about 20 volumes of water and foamed to provide avolume expansion of from about 5 to about 40 times the volume of theunfoamed material.
 10. The method of claim 1 wherein the foaming agentis at least one nonionic surfactant.
 11. The method of claim 10, inwhich the nonionic surfactant comprises at least one of alkanolamines,aminoxides, ethoxylated alcohols, ethoxylated alkylphenols, ethoxylatedesters, glucose esters, sucrose esters or derivatives thereof.